lift pump location question

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gadget73
Posts: 1199
Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

lift pump location question

Post by gadget73 »

ok not location in the physical sense, but in the flow sense
Ford plumbs the fuel system as tank -> filter -> low pressure pump -> injection pump.
My understanding is that US BMW has a lift pump in the tank, so its tank -> pump -> filter -> injection pump.
Euro I think does not have a lift pump at all?

would there be any advantage to moving my lift pump to before the filter? Physically its up front, mounted along side the engine just below the lift pump and I have no plans to move it but I don't mind shuffling the hoses around.

Reason I ask, the car has always had something of a flat spot on hard acceleration. It winds up and then just sort of stops other than random little "nudges" until it finally decides to upshift. I realize its not exactly powerful but it feels like its running out of fuel. No smoke, and the injection pump has been tweaked up a bit. Its done this as long as I have owned the car, both before and after the injection pump rebuild. I'm thinking maybe the lift pump can't draw fuel through the filter effectively. Changing the filter didn't do anything for it.


my next step is to tee in a pressure gauge between the lift pump and the injection pump to see if the pressure drops to zero when it seems to lose power. If it does that makes me think either there is a restriction in the supply, or that little pump just can't keep up. Its not original but I have no idea what it is. It sure looks like any generic round 12v fuel pump you can find at an auto parts store meant to be used with a carb.
gadget73
Posts: 1199
Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

Re: lift pump location question

Post by gadget73 »

as usual, over-thinking the problem. the lift pump wasn't even running. Someone suggested I check it, and when I reached in there it kicked on when I bumped the wiring. One terminal had pulled out of the relay, and it would make random contact. jammed it back in and its running normally now. Will replace the relay socket and it should be good. The latch finger is busted.
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